This invention relates generally to tubular pipe assemblies for hot or cold fluid transfer which assemblies include a plurality of insulated conduit sections and more particularly to a new and improved oil well casing assembly and coupler therefore, for oil well steam injection or above ground transport of process fluids under high pressure and elevated temperature. The assembly provides for a minimum heat and pressure loss, withstands multiple coupling and uncoupling operations in the field without deterioration of the insulated conduit sections, prevents the contamination of the insulation within the conduit sections if and when a coupling fails, provides for a relatively cool-threaded mechanical joint between the conduit sections and is capable of being readily repaired in the field.
In the past, attention was given primarily to insulating the hot process fluid from the surrounding environment during transport through a conduit, such as injecting steam through the conduit into an oil well. This was accomplished by inserting a smaller pipe within a larger diameter pipe and insulating the annular cavity between the pipes. The outer pipes usually had externally threaded ends so that an internally threaded coupling or sleeve would join two conduit sections together. The inner pipes were sealed from the environment by a seal. The transportation of a higher temperature fluid under a greater pressure with the ability to force more oil from the well created a problem relating to the thermal expansion and contraction of the inner pipe with respect to the outer pipe. One solution to this problem was to telescope the ends of the inner pipes relative to one another and allow enough space for the pipes to longitudinally expand. Another solution to this expansion/contraction problem was to prestress the inner pipe by heating it and immediately welding the expanded inner pipe to the outer pipe. A third solution employed two rigid members, usually frusto-conical in shape, at each end of the conduit which placed the inner pipe under compression or tension, depending on whether the pipe would carry hot or cold process fluids. The frusto-conical member translates the tension/compression forces, generated by the contraction/expansion of the inner pipe to the outer pipe. These developments focused upon the dynamics of the pipes within the insulated conduits, vis-a-vis, the temperature of the process fluids. The art did not address the problems relating to the joining of the insulated conduit sections. An internally threaded coupling or sleeve was used to join the insulated conduit sections in conjunction with most of the above-described devices. This joining was accomplished by manipulating the conduit sections and the single coupling at the site of the oil well with field tools or oil well rig tongs. The manipulation of the outer pipes of the insulated conduit section caused the outer pipes to deteriorate after multiple coupling and uncoupling operations. The heat loss through the single coupling lowered the over-all efficiency of the tubular assembly and the transfer of heat through the single coupling hastened the deterioration of the coupling threads and the outer pipe threads.
A primary objective of the present invention is, therefore, to provide an improved high temperature and high pressure tubular pipe assembly which includes a plurality of insulated conduit sections joined together by male and female couplings for transporting hot process fluids and which assembly minimizes the loss of heat and pressure through the tubular assembly and withstands multiple coupling and uncoupling operations in the field without deterioration of the outer pipes of the insulated conduit sections. The male and female couplings are directly manipulated by the field tools or oil well rig tongs during the coupling and uncoupling operations rather than the conduit sections being manipulated by the tools.
Another object of the present invention is to provide a tubular assembly wherein the mechanical, threaded joint between the male coupling and the female coupling, which join two conduit sections together, is thermally insulated from the hot process fluids which are transported through the inner pipes.
Another object of the present invention is to provide a joint between two conduit sections that can withstand the additional forces developed by the expansion and contraction of the inner pipes which carry the process fluids.
Another object of the present invention is to provide a male and female coupling for insulated conduit sections which couplings do not affect the integrity of the insulation within the conduit sections if and when the male or female coupling fails.
Another object of the present invention is to provide a tubular assembly with a coupling wherein the coupling can be repaired in the field.